Causes and consequences of dispersal

Collective dispersal occurs when individuals disperse away from the location of birth but recruit in aggregations. A wide range of taxa disperse collectively, including plants, marine and terrestrial arthropods, fish, birds, and mammals. Observations of collective dispersal challenge predictions from theory on the adaptive value of dispersal. This is because individuals are not distributed as current dispersal theory predicts would happen if there is selection to spread kin in order avoid competition, inbreeding, or unpredictable environmental variation. If dispersal is an adaptation to spread kin in space, then why do we see collective dispersal in nature? To what extent is collective dispersal determined by adaptive or non-adaptive processes, and how does it influence selection on the spatial patterns of dispersal and the traits that influence movement? In marine bryozoans (‘plant-like animals’), we are empirically estimating the spatial scales at which reproduction, competition, and environmental variation occur relative to the spatial scales at which organisms move, coupled with estimates of the whether proximity to kin and conspecifics increases or decreases fitness.

Robin Snyder and I are looking at how turbulent eddies in coastal environments might act as an agent of selection on some aspects of marine life cycles involving a pelagic larval stage and a benthic adult stage. Nearshore turbulence can collect larvae into ‘packets’ causing siblings to succeed or fail as a group (by whether or not they encounter settlement habitat). This results in a form of within generation variance in fitness. How do marine life histories reduce this risk of complete brood failure? Is it better to increase mean fitness or to reduce the variance in fitness (‘bet hedge’)? We have developed mathematical models that predict how turbulent dispersal favors reducing the variance fitness (rather than increasing mean fitness) by selecting for longer spawning periods and offspring sizes that are different to the ‘optimal’ size in less stochastic environments.


Size-dependent physiology and demography of corals 

I am collaborating with Pete Edmunds to explicitly link metabolic scaling and population dynamics to better understand the mechanisms driving coral community structure and change. We are using Integral Projection Models to combine detailed physiological experiments with long-term survey data from several coral populations at Moorea, French Polynesia (collected as part of the Moorea LTER). As part of this effort, we are also investigating the ‘hidden’ functional and demographic differences between several clades of Pocilloporid corals that are genetically distinct but sometimes morphologically indistinguishable.


Environmental predictability and adaptive maternal effects

Maternal effects occur when the environment or phenotype of the mother causes the phenotype of their offspring. Maternal effects are adaptive when mothers respond to a cue that predicts future selection on the offspring phenotype and adjusts the phenotype of their offspring in the direction favored by selection. We are studying how fluctuations in water temperature influence both the strength of the cue to mothers, the offspring phenotype,  and the pattern of selection on offspring traits such as larval size or settlement behavior.